Vehicular heating and air-conditioning systems are known wherein independent dual temperature control is provided. For example, heavy-duty trucks such as large tractor trailer vehicles have independent temperature control for a cab area and a bunk area. Indeed, even smaller vehicles are known to provide independent temperature control in a forward cab area and rear cab area.
In a typical automotive heating and air-conditioning system, a control panel is provided in the passenger compartment or cab area of the vehicle, and provides independent control over the fan speed as well as the air temperature. For example, a multi-position switch is commonly provided to allow selection among multiple fan speeds. A rheostat or other continuously variable control provides variable control over the air temperature selection. In vehicles having independent dual temperature control, separate controls are provided for independently controlling the operation of the blower fans and air temperature.
As is known, heat control is achieved by circulating water from the vehicle's cooling system through a set of heating coils, and air-conditioning is provided by circulating refrigerant through an evaporator, also known as cooling coils. Both the heating and cooling coils are typically disposed within a common housing. A blower is attached to the housing (blower unit) and is disposed to control the air flow through the system, as determined by the fan speed selected by a user or passenger. Air drawn by the blower across the heating coils delivers warm air to the cab of the vehicle, while air drawn across the cooling coils delivers cool air to the vehicle cab space. Air temperature control is provided by regulating the quantity of air that flows across either the cooling coils, the heating coils, or both.
Typically, the air drawn by the blower unit is directed across the cooling coils, to prevent the coils from freezing. Thus, temperature control is usually achieved by regulating the air flow across the heating coils. As warmer air is desired, a greater amount of air is directed across the heating coils. As cooler air is desired, a smaller amount of air is directed across the heating coils.
In a dual control system, having independent temperature and fan speed control, two separate blower units are provided, each having its own heating coils and cooling coils. As can be appreciated, this increases both the cost and complexity of the system. Significantly, two sets of heating coils and two sets of cooling coils are required. Also, additional connectors and fluid cabling, such as heater hose and refrigerant tubing are needed. This approach further dictates that additional space requirements are needed for the second blower unit, and this additional space requirement becomes particularly significant in dual control applications on smaller vehicles where space conservation is a significant aspect.
In view of the foregoing, a simpler and therefore more cost effective dual control vehicular ventilation system is desired.